US4257679A - Reproducing objective for video disks - Google Patents

Reproducing objective for video disks Download PDF

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Publication number
US4257679A
US4257679A US06/064,870 US6487079A US4257679A US 4257679 A US4257679 A US 4257679A US 6487079 A US6487079 A US 6487079A US 4257679 A US4257679 A US 4257679A
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United States
Prior art keywords
sub
reference symbol
respectively represent
lenses
lens
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US06/064,870
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English (en)
Inventor
Kaneyas Okawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Olympus Corp
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Olympus Optical Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Olympus Optical Co Ltd filed Critical Olympus Optical Co Ltd
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Publication of US4257679A publication Critical patent/US4257679A/en
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
    • G02B9/34—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having four components only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B13/00—Optical objectives specially designed for the purposes specified below
    • G02B13/24—Optical objectives specially designed for the purposes specified below for reproducing or copying at short object distances
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1374—Objective lenses
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372—Lenses
    • G11B7/1378—Separate aberration correction lenses; Cylindrical lenses to generate astigmatism; Beam expanders
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive

Definitions

  • the present invention relates to an objective for video disks and, more particularly to an objective for reading out the signals recorded on high-density information-recording disks (video disks).
  • the objective For objectives to be used in reproducing systems for video disks, it is required to warrant resolving power of 1 ⁇ due to the fact that the objective has to read out very small signals recorded with high density.
  • the information read out from the disk, which rotates at high speed contains signals for making the objective follow up the recorded track and signals for automatic focusing in addition to image information.
  • the flatness of image focused by the objective should be high.
  • the working distance of the objective should be long.
  • the objective should be compact and light in weight.
  • the price of the objective should be low.
  • the working distance should be long enough for protecting the surface of video disk.
  • the working distances are 0.26f to 0.36f and these values are smaller than the required value.
  • the objectives for video disks should be low in price. But, the known objectives for video disks are not satisfactorily low in price.
  • a primary object of the present invention to provide a reproducing objective for video disks which has high resolving power equal to or higher than the known objective for video disks, the working distance of which is longer than the known objectives and in which respective lenses constituting the lens system are arranged so that the objective can be produced at low cost.
  • the reproducing objective for video disks according to the present invention are arranged so that some of lenses constituting the lens system have flat surfaces on one side in order to reduce the cost of production. That is, the reproducing objective for video disks according to the present invention comprises a first, second, third and fourth lenses in the other from the reproducing light source side, the first lens being a plano-convex lens, the second lens being a plano-concave lens, the third lens being a positive lens, the fourth lens being a positive meniscus lens.
  • the objective for video disks according to the persent invention satisfies the following conditions.
  • reference symbol f represents the focal length of the lens system as a whole
  • reference symbols f 1 , f 2 and f 4 respectively represent the focal lengths of the first, second and fourth lenses
  • reference symbol r 2 represents the radius of curvature of the surface on the disk side of the first lens
  • reference symbol r 4 represents the radius of curvature of the surface on the disk side of the second lens
  • reference symbol r 8 represents the radius of curvature of the surface on the disk side of the fourth lens
  • reference symbol d 2 represents the airspace between the first and second lenses
  • reference symbol d 4 represents the airspace between the second and third lenses.
  • the condition (1) relates to spherical aberration of the first lens.
  • Astigmatism which is caused by the third and fourth lenses, by means of the other lenses so that astigmatism of the lens system as a whole is corrected favourably, the shape of the first lens is restricted to some extent.
  • spherical aberration is caused by the first lens.
  • the condition (1) relates to the above-mentioned spherical aberration. If, in this condition, f 1 becomes smaller than 1.7f, negative spherical aberration to be caused by the first lens becomes too large and it will be impossible to correct it by the other lenses.
  • the condition (2) is established for the purpose of making the second lens cause positive spherical aberration of adequate value in order to thereby correct negative spherical aberration which occurs at the first lens. If the focal length f 2 of the second lens becomes smaller than -4.3f, spherical aberration of the lens system as a whole will be undercorrected. If, on the contrary, f 2 becomes larger than -3.5f, spherical aberration of the lens system as a whole will be overcorrected.
  • the condition (3) is established for the purpose of correcting astigmatism. If, in the condition (3), f 4 becomes smaller than 1.4f, astigmatism will be undercorrected. If, on the contrary, f 4 becomes larger than 1.9f, astigmatism will be overcorrected.
  • the conditions (4) and (5) are established for the purpose of producing the lenses easily by arranging the surfaces on the disk side of the first and second lenses as flat surfaces. Thus, it is possible to produce the lenses at low cost, which is one of objects of the present invention.
  • the condition (6) relates to curvature of field.
  • r 8 of the surface on the disk side of the fourth lens it is advantageous for making the working distance long. That is, the working distance becomes longer when r 8 is made smaller. If, however, r 8 is made too small and it becomes r 8 >0.5f, curvature of field will be overcorrected. If, on the other hand, r 8 becomes larger than 1.7f, curvature of field will be undercorrected.
  • the condition (7) is established on the premise that the circumferential portion of the surface on the light source side of the second lens is to be kept in direct contact with the flat surface of the first lens. When this condition is satisfied, it is not necessary to insert a spacer ring between the first and second lenses and, therefore, it is possible to assemble the lenses to the design value accurately and easily. Moreover, by the condition (7) in combination with the fact that the surfaces on the disk side of the first and second lenses are respectively arranged as flat surfaces as defined by the conditions (4) and (5), it is possible to adjust the alignment of lenses in the lens system very easily. As explained in the above, the conditions (4), (5) and (7) are established for the purposes of reducing the number of parts and number of processes, simplifying the manufacturing work, enabling to easily manufacture to the design value, reducing the price and so forth.
  • the lens system as a whole becomes more compact when the airspace d 4 between the second and third lenses is smaller. If, however, it becomes d 4 >0.6f, coma and curvature of field will be caused and it will become impossible to correct them by the other surfaces.
  • d 4 is made larger, it is possible to make the working distance longer.
  • the working distance is 0.3f to 0.5f.
  • FIG. 1 shows a sectional view of the reproducing objective for video disks according to the present invention.
  • FIGS. 2 through 8 respectively show graphs illustrating aberration curves of respective embodiments of the present invention.
  • reference symbols r 1 through r 8 respectively represent radii of curvature of respective lens surfaces
  • reference symbols d 1 through d 7 respectively represent thicknesses of respective lenses and airspaces between respective lenses
  • reference symbols n 1 , n 2 , n 3 and n 4 respectively represent refractive indices of respective lenses at the wavelength of 632.8 nm
  • reference symbols ⁇ 1 , ⁇ 2 , ⁇ 3 and ⁇ 4 respectively represent Abbe's numbers of respective lenses for d-line
  • reference symbol W.D reference symbol
  • reference symbol t represents the thickness of the cover glass C
  • reference symbol n t represents the refractive index of the cover glass C
  • reference symbol f represents the focal length of the lens system as a whole
  • reference symbols f 1 , f 2 , f 3 and f 4 respectively represent the focal length of the first, second, third and fourth lenses
  • reference symbol ⁇ represents magnification
  • reference symbol N.A. represents the numerical aperture on the disk side
  • reference symbol ⁇ d represents the overall length of lens system.
  • Embodiment 7 is arranged so that the surface r 6 on the disk side of the third lens also becomes a flat surface in addition to the flat surfaces of the first and second lenses and, therefore, it is more convenient for manufacture.

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Lenses (AREA)
  • Optical Head (AREA)
US06/064,870 1978-08-17 1979-08-08 Reproducing objective for video disks Expired - Lifetime US4257679A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP9945878A JPS5526545A (en) 1978-08-17 1978-08-17 Reproducing lens for video disc
JP53-99458 1978-08-17

Publications (1)

Publication Number Publication Date
US4257679A true US4257679A (en) 1981-03-24

Family

ID=14247865

Family Applications (1)

Application Number Title Priority Date Filing Date
US06/064,870 Expired - Lifetime US4257679A (en) 1978-08-17 1979-08-08 Reproducing objective for video disks

Country Status (3)

Country Link
US (1) US4257679A (enrdf_load_stackoverflow)
JP (1) JPS5526545A (enrdf_load_stackoverflow)
DE (1) DE2932981C2 (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4332442A (en) * 1979-05-04 1982-06-01 Olympus Optical Co., Ltd. Reproducing objective for video disks
US4368957A (en) * 1980-10-31 1983-01-18 Discovision Associates Wide aperture objective lens
US4416519A (en) * 1980-09-02 1983-11-22 Olympus Optical Co., Ltd. Objective for video disks
US4484802A (en) * 1981-09-07 1984-11-27 Olympus Optical Co., Ltd. Optical read-out lens system for optically recorded disks
US4523817A (en) * 1981-11-18 1985-06-18 Olympus Optical Co., Ltd. Lens system for optically recorded disks
US4743094A (en) * 1984-11-29 1988-05-10 Lockheed Missiles & Space Company, Inc. Finite conjugate imaging system
US20040051957A1 (en) * 2002-08-06 2004-03-18 Dmetrix, Inc. Miniature microscope objective lens
FR2845488A1 (fr) * 2002-10-08 2004-04-09 Trophos Dispositif optique pour l'observation d'echantillons sur un support, destine notamment a un cytometre

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3220408C2 (de) * 1982-05-29 1985-05-15 Optische Werke G. Rodenstock, 8000 München Abtastobjektiv
DE4030344C3 (de) * 1990-09-26 1996-09-26 Battelle Ingtechnik Gmbh Verfahren und Vorrichtung zum Sortieren von vereinzelbaren, kleineren Gegenständen, insbesondere Früchten aller Art

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3915559A (en) * 1974-10-15 1975-10-28 Bell & Howell Co Short focal length large aperture optical system
US3942877A (en) * 1974-11-11 1976-03-09 Bell & Howell Company Short focal length Petzval-type optical system
US3944338A (en) * 1974-11-11 1976-03-16 Bell & Howell Company Short focal length long back focus objective

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3915559A (en) * 1974-10-15 1975-10-28 Bell & Howell Co Short focal length large aperture optical system
US3942877A (en) * 1974-11-11 1976-03-09 Bell & Howell Company Short focal length Petzval-type optical system
US3944338A (en) * 1974-11-11 1976-03-16 Bell & Howell Company Short focal length long back focus objective

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4332442A (en) * 1979-05-04 1982-06-01 Olympus Optical Co., Ltd. Reproducing objective for video disks
US4416519A (en) * 1980-09-02 1983-11-22 Olympus Optical Co., Ltd. Objective for video disks
US4368957A (en) * 1980-10-31 1983-01-18 Discovision Associates Wide aperture objective lens
US4484802A (en) * 1981-09-07 1984-11-27 Olympus Optical Co., Ltd. Optical read-out lens system for optically recorded disks
US4523817A (en) * 1981-11-18 1985-06-18 Olympus Optical Co., Ltd. Lens system for optically recorded disks
US4743094A (en) * 1984-11-29 1988-05-10 Lockheed Missiles & Space Company, Inc. Finite conjugate imaging system
US20040051957A1 (en) * 2002-08-06 2004-03-18 Dmetrix, Inc. Miniature microscope objective lens
US7023622B2 (en) * 2002-08-06 2006-04-04 Dmetrix, Inc. Miniature microscope objective lens
FR2845488A1 (fr) * 2002-10-08 2004-04-09 Trophos Dispositif optique pour l'observation d'echantillons sur un support, destine notamment a un cytometre
WO2004034122A3 (fr) * 2002-10-08 2004-05-27 Trophos Dispositif optique pour l'observation d'echantillons sur un support, destine notamment à un cytometre

Also Published As

Publication number Publication date
JPS6136207B2 (enrdf_load_stackoverflow) 1986-08-16
DE2932981C2 (de) 1983-02-10
DE2932981A1 (de) 1980-02-21
JPS5526545A (en) 1980-02-26

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